Unique Isothermal Crystallization Behavior of Novel Polyphenylene

J. Phys. Chem. B 2008, 112, 14819–14828

14819

Unique Isothermal Crystallization Behavior of Novel Polyphenylene Sulfide/Inorganic Fullerene-like WS2 Nanocomposites Mohammed Naffakh,*,† Carlos Marco,† Mariań A. Go´mez,† and Ignacio Jimeńez‡ Departamento de Fı´sica e Ingenierıá de Polı´meros, Instituto de Ciencia y Tecnologıá de Polı´meros, CSIC, c/Juan de la CierVa, 3, 28006 Madrid, Spain, and Instituto de Ciencia de Materiales de Madrid, CSIC, Campus de Cantoblanco, 28049 Madrid, Spain ReceiVed: July 17, 2008; ReVised Manuscript ReceiVed: September 10, 2008

The isothermal crystallization of polyphenylene sulfide (PPS) nanocomposites with inorganic fullerene-like tungsten disulfide nanoparticles (IF-WS2) has been studied from a thermal and morphological point of view, using differential scanning calorimetry (DSC), scanning electron microscopy (SEM), polarized optical microscopy (POM) and time-resolved synchrotron X-ray diffraction. All the analyses revealed that the incorporation of the IF-WS2 altered significantly the crystallization behavior of PPS, in a way strongly dependent with the nanocomposite composition. The addition of IF-WS2 in 0.1 wt % proportion retarded the crystallization of PPS by increasing its fold surface free energy in a 10%. However, addition of the nanoparticles in excess of 1 wt % results in a promotion of the crystallization rate with reduction of the fold surface free energy to half the value of pure PPS. Introduction During the last years, a number of efforts have been made to develop high-performance polymeric materials with the benefit of new nanoparticle fillers in fields ranging from the basic scientific interest to the industrial application. The continuous progress in nanoscale control as well as an improved understanding of the physicochemical properties of nanocomposite materials have contributed to the rapid development of polymer nanocomposites. Inorganic fullerene-like materials (IF) like WS2 (IF-WS2), which were discovered by Tenne in 1992,1 have recently gained new research interest through their use as nanoparticles to prepare new types of polymer composites. These IF particles exibit outstanding properties, such as high modulus and low friction coefficient, attributed to their small size, closed structure, and chemical inertness. Depending upon the target properties, a variety of matrices have been explored, including epoxy,2 isotactic polypropylene,3 or PEEK.4 Considerable improvement has been achieved on the mechanical and tribological properties of these nanocomposites. Poly(phenylene sulfide) (PPS) is well known as one of the high-performance semicrystalline aromatic polymer with outstanding high-temperature stability, good chemical and flame resistances, excellent electrical insulation, antiaging, and precision moldability.5,6 However, the application of neat PPS has been limited because of its relatively low glass transition (Tg) compared to the high melting temperature (Tm) and its brittleness. To overcome these drawbacks, commercial PPS grades are usually filled with different materials like glass fibers.7 In this sense, the combination of PPS and IF-WS2 nanoparticles is expected to provide also superior properties. However, the ultimate properties of composite materials based on a crystallizable matrix are largely determined by the crystalline morphology of the polymer matrix, which depends on the nucleation * To whom correspondence should be addressed. E-mail: mnaffakh@ ictp.csic.es. † Instituto de Ciencia y Tecnologıá de Polı´meros, CSIC. ‡ Instituto de Ciencia de Materiales de Madrid, CSIC.

and crystallization growth rates that define the crystallization kinetics. The nucleation and growth processes are governed by the thermal and mechanical processing conditions that are used as well as by the presence of the filling nanoparticles. The main objective of this study is to understand the effect of IF-WS2 nanoparticles on the crystallization behavior of meltprocessed PPS/IF-WS2 nanocomposites under isothermal crystallization conditions. The nanocomposites were prepared by melt-mixing as the most simple and effective method from both an economic and industrial perspective, because this process makes possible to fabricate high-performance nanocomposites at low cost and facilitates commercial scale-up. Experimental Section Materials and Processing. PPS (Fortron 02054P4) was supplied in pellet form by Ticona. The IF-WS2 nanoparticles (NanoLub) with an average diameter of 80 nm3 were provided by Nanomaterials (in Israel, ApNano Materials in U.S.A.). The thermoplastic polymer was dried at 100 °C for 14 h before use to minimize the effects of moistures. Several concentrations of IF-WS2 (0.1, 1, and 2 wt %) were introduced in the PPS matrix by melt-mixing using a Haake Rheocord 90 system operated at 320 °C and a rotor speed of 150 rpm for 20 min. Characterization Techniques. The dispersion of IF-WS2 on PPS matrix was characterized using a Philips XL30 ESEM scanning electron microscope (SEM) equipped with an energy dispersive X-ray (EDX) EDAX superUTW microanalytical system. The polymer samples were cryo-fractured from film specimens and then were placed in a heated oven for 2 h at 200 °C in order to better identify the IF-WS2 nanoparticles in the PPS matrix. The fractured samples were coated with a ∼5 nm Au/Pd overlayer to avoid charging during electron irradiation. Polarized optical microscopy (POM) was used to investigate the spherulitic morphology of PPS nanocomposites by using a Reichert Zetipan Pol polarizing microscope and a Mettler FP80HT hot stage with a Nikon FX35A 35-mm SLR camara. The nanocomposite thin films (∼15 µm) were sandwiched between

10.1021/jp8063245 CCC: $40.75  2008 American Chemical Society Published on Web 10/28/2008

14820 J. Phys. Chem. B, Vol. 112, No. 47, 2008

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Figure 1. SEM micrographs of (a) PPS/IF-WS2 (0.1 wt %) and (b) PPS/IF-WS2 (1 wt %) nanocomposites; inset is the SEM micrograph obtained at higher magnification.

two glass slides and isothermally crystallized at a fixed temperature after cooling at 20 °C min-1 from the melt. The isothermal crystallization behavior of PPS nanocomposites was investigated using a Perkin-Elmer DSC7/UNIX/7DX differential scanning calorimeter. From the evolution of the exotherms during crystallization, the kinetics of crystallization was evaluated. In each DSC run, about 12 mg sample, which had been held at 320 °C for 5 min to eliminate previous thermal history, was isothermally crystallized at a fixed temperature and subsequently heated at a rate of 5 °C min-1 to 320 °C under nitrogen atmosphere. Partial areas, corresponding to a given percentage of the total transformation, were determined from the data points stored on a PE 7700 computer, using Pyris DSC7 kinetic software. For the estimation of the crystallinity of the samples, a value of 80 J g-1 for the melting enthalpy of 100% crystalline PPS was used.8 Small and wide-angle X-ray scattering (SAXS/WAXS) experiments using synchrotron radiation were performed at the A2 beamline of the HASYLAB synchrotron facility (DESY, Hamburg). The experiments were performed with monochromatic X-rays of 0.15 nm wavelength using a germanium single crystal as the dispersing element. The scattering was detected

with a linear Gabriel detector. The sample to detector distance of SAXS was 2315 mm and for WAXS was 135 mm. The scattering angle of the SAXS pattern was calibrated with the RTT (rat tail tendon), and that of the WAXS profile was calibrated with a PET standard. The maximum of the Lorentzcorrected SAXS diffractograms was used to calculate the long period (L ) 1/smax) as a function of the temperature. L represents the sum of the average thickness of the crystal lamellae and of the interlamellar amorphous regions. The methodology used in the isothermal crystallization experiments of the nanocomposites by SAXS/WAXS was similar to that described for the calorimetric experiments. Measurements were performed with acquisition time of 60 s (wait time ) 50 s and read time ) 10 s) and 24 s (wait time ) 14 s and read time ) 10 s) for isothermal crystallization and subsequent melting, respectively. Results and Discussion Dispersion of IF-WS2 in the PPS Matrix. The dispersion of IF-WS2 nanoparticles in the PPS matrix at the nanoscale is one of the most important features in advanced polymer nanocomposites. SEM observation is used to directly and

PPS Nanocomposites with Inorganic Fullerence-like WS2

J. Phys. Chem. B, Vol. 112, No. 47, 2008 14821

Figure 2. Plots of DSC curves of (a) PPS, (b) PPS/IF-WS2 (0.1 wt %), and (c) PPS/IF-WS2 (1 wt %) under isothermal crystallization conditions; insets are the plots of crystalline conversion (θ) versus time.


Naffakh et al.

Figure 3. Time to attain an i degree of transformation of PPS/IF-WS2 nanocomposites as a function of the crystallization temperature: (a) i ) 10% and (b) i ) 2%.

qualitatively visualize the state of dispersion of IF-WS2 nanoparticles in the PPS matrix. Figure 1 shows the SEM image of fractured surfaces of PPS/IF-WS2 nanocomposites in which the bright spots are the cross section of the IF-WS2 nanoparticles in the whole examined area. The SEM analysis reveals that the IF-WS2 appear as small aggregates of only a few particles. The average diameter of IF-WS2 in the matrix, calculated from five SEM images for each sample, was found to be around 180 nm in contrast to the average value of 80 nm for the individual IF particles.3 The dispersion state of IF-WS2 in the PPS matrix was the key parameter for drastic improvements of the mechanical properties of PPS.9 Isothermal Crystallization Kinetics. The understanding of the crystallization behavior of the nanocomposites is very important in order to optimize the processing conditions and to control the structure, physical, and final properties of the polymeric materials. It is well known that polymer crystallization is due to homogeneous, heterogeneous, or self-nucleation processes followed by the growth of the crystals with crystallization time. Therefore, the overall crystallization behavior of polymers can be analyzed by the observation of the rates of nucleation and growth or by the overall rate of crystallization. Figure 2 shows the isothermal exothermic curves of PPS and its nanocomposites obtained by cooling from the melt to the

crystallization temperature (Tc). It can be observed that the crystallization of PPS nanocomposites is strongly affected by Tc. With increasing Tc, the exotherm peak at which the highest crystallization rate is reached shifts to a longer time value, the crystallization exotherm becomes flatter, and the time to reach the maximum degree of crystallization (see insert) increases. All of the above indicate that the crystallization rate decreases with increasing Tc. However, the most relevant observation was the influence of IF-WS2 concentration on the time of crystallization of PPS for a particular Tc. In panel b of Figure 2, it is shown that the addition of 0.1 wt % of IF-WS2 reduces the crystallization rate of PPS, which implies that the nucleation of PPS crystals is retarded by the IF-WS2 nanoparticles. This observation is quite uncommon compared with the effect of other nanofillers on polymer crystallization. However, in panel c of Figure 2, it is shown that the increase of the IF-WS2 concentration to 1 wt % induces an increase in crystallization rate of PPS. This implies that IF-WS2 is now acting as a nucleating agent for PPS. The dependence of crystallization rate of PPS on the crystallization temperature and composition is clearly observed in the data represented in Figure 3. The time to reach 10% of transformation (τ0.1) of PPS, calculated from the partial areas of each exothermic curve, increased exponentially with temperature, confirming that the ordering process



Figure 4. Avrami plots of the crystallization of (a) PPS/IF-WS2 (0.1 wt %) and (b) PPS/IF-WS2 (2 wt %) as a function of the crystallization temperature.

Figure 5. Logaritmic plots of the rate constant (kn) of PPS/IF-WS2 nanocomposites as a function of the crystallization temperature.


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Figure 6. DSC thermograms of (a) PPS, (b) PPS/IF-WS2 (0.1 wt %), and (c) PPS/IF-WS2 obtained at a heating rate of 5 °C min-1 after isothermal crystallization at the indicated temperatures.


Figure 7. WAXS diffractograms of PPS/IF-WS2 (1 wt %) nanocomposite obtained at a heating rate of 5 °C min-1 after isothermal crystallization at 260 °C.

occurred through a nucleation mechanism. Our second observation is related with the strong influence of IF-WS2 on the crystallization temperature range of PPS. And finally, the dependence of crystallization rate of PPS on composition is also observed in the variation of the values of τ0.1 of PPS for indicated Tc. This fact is also observed when crystallinity starts to develop, even at the lowest level of 2% of transformation, which indicates that the differences in the crystallization rate of PPS with different IF-WS2 content are controlled, mainly by the nucleation process. The crystallization kinetics of polymers under isothermal crystallization conditions for various modes of nucleation and growth can be approximated by the well-known Avrami equation.10 Although the Avrami equation is widely discussed and often its kinetic parameters loose the physical meaning attributed by the theory, nevertheless it is still generally adopted for the treatment of the experimental data, including only the initial part of the process. However, experimental kinetical parameters are also accounted by mixed growth (presence of bidimensional sheaflike structures together with three-dimensional spherulite structures) and/or surface nucleation modes and secondary crystallization process.11-14 The differences in the experimental procedures employed (e.g., dwelling time and melting temperature) and in the chemical nature of materials (molecular weight, polydispersity, chemical nature of the endgroup counter atom, and branching) may also explain the wide range of variability on the calculation of the kinetic paramaters.11,15,16 Figure 4 shows the typical Avrami plots (log[-ln(1 - θt)] vs log t) corresponding to PPS/IF-WS2 nanocomposites. It can be seen that each curve shows an almost linear relationship, indicating that the Avrami approximation can properly describe the isothermal behavior in the range of 5-35% crystalline transformation. An average value of the Avrami exponent around 4 was obtained for PPS/IF-WS2 nanocomposites from the slope

J. Phys. Chem. B, Vol. 112, No. 47, 2008 14825 of these fit lines, suggesting that the crystallization may involve homogeneous nucleation with three-dimensional growth. The second parameter determined from the crystallization kinetic analysis was the global rate constant of the crystallization process (kn) based on the well-fitting logarithmic representation of equation kn ) ln 2/(τ0.5)n as shown in Figure 5.17 Additionally, it can be seen that kn values of PPS are influenced by the IFWS2 content. As an example, neat PPS presented a kn of around 1.0 × 10-4 for Tc of 264 °C; in the case of the nanocomposites the kn values at the same temperature change with the IF-WS2 concentration as follows: 4.5 × 10-6 for 0.1 wt %, 1.9 × 10-3 for 1 wt %, and 2.1 × 10-2 for 2 wt %. These results show again that the IF-WS2 nanoparticles play a key role as retarders or promoters of the PPS nucleation depending on the concentration of particles in the PPS matrix. Melting Behavior. PPS displays multiple endotherms on a heating run in a DSC, which has been usually interpreted in terms of a pre-exiting morphology and/or reorganization as reported for other polymers such as PEEK.14,18-21 Both reasons often compete with each other to make the melting behavior very complex, and sometimes it is very difficult to differentiate between these two effects. A detailed review on the melting mechanisms in semicrystalline polymers has been published in ref 22. Figure 6 shows the DSC melting curves obtained after isothermal crystallization at different Tc for PPS and the nanocomposites. Two melting peaks defined as TmI (low temperature peak) and TmII (high temperature peak) are always present during heating. These melting peaks are related to the melting of PPS crystals with an unique crystalline structure as shown in the synchrotron WAXS experiments presented in Figure 7. The two diffraction peaks appear at 2θ angles of 18.5 and 20.5° corresponding to the (110) and (200) planes of the orthorombic structure.23 It is clear from Figure 6 that both melting peaks shift to higher temperature with increasing Tc, which are directly related to the perfection of the pre-existing PPS crystals formed at Tc. However, the existence of melting-recrystallizationmelting phenomena during heating cannot be excluded from the observation of the DSC melting curves, as reported previously.19,20 It is also important to note that the melting behavior of PPS/IF-WS2 nanocomposites are controlled by the crystallization kinetics. The results obtained show that the reduction of the crystallization rate of PPS maximize the effect of perfection or thickening of the lamellae of the more imperfect crystals. Thus, the TmI shifts to higher temperature with adding IF-WS2 (0.1 wt %). At this concentration, the long period (L) of dual crystal populations shows higher values, especially at higher heating temperatures, as shown in Figure 8. It can also be suggested that the reorganization of PPS crystals during the heating is hindered with the increase of the IF-WS2 content (1 wt %). Thus, the values of L of the PPS/IF-WS2 (1 wt %) are lower than those of PPS. The kinetic data obtained by calorimetry were also analyzed from a thermodynamic point of view. The data of melting endothemic peaks as a function of Tc are plotted in Figure 9. The equilibrium melting point (Tom) is obtained by extrapolation of the resulting straight line to intersect the line Tm ) Tc. The extrapolation of the variation of the apparent melting temperature (TmII) to the line corresponding with Tm ) Tc with little dispersion led to a value of 320 °C, which can be considered the Tom of the PPS/IF-WS2 nanocomposites. Crystallization Activation Energy. The crystallization thermodynamics and kinetics of the PPS/IF-WS2 nanocomposites have been analyzed according to the well-known Lauritzen and


Naffakh et al.

Figure 8. Long period (L) values of PPS/IF-WS2 nanocomposites obtained at a heating rate of 5 °C min-1 after isothermal crystallization at 260 °C.

Figure 9. Plots of the observed melting temperatures (TmI and TmII) of PPS/IF-WS2 nanocomposites as a function of crystallization temperature.

Hoffmann (LH) equation.24,25 The spherulitic radial growth rate G (defined as G ) 1/τ0.1) depends on the Tc as stated by the following expression:

[

G ) G0 exp -

] [

Kg U* exp R(Tc - T0) fTc∆T

]

(1)

where G0 is a pre-exponential term, independent of temperature. In the first exponential, representing the diffusional contribution to the growth rate, U* is the activation enery needed for the chains movement, T0 represents the temperature at which they are motionless, and R is the universal gas constant. In the second exponential Kg ) jb0σσe/∆hfR, where j is a variable that considers the crystallization regime and assumes the value j ) 4 for regime I and III and j ) 2 for regime II, b0 is the distance between two adjacent fold planes, σ and σe are the free energies per unit area of the surfaces of the lamellae parallel and perpendicular to the chain direction, respectively, ∆hf is the equilibrium melting enthalpy, and kB is the Boltzmann

constant, ∆T ) Tom - Tc is the supercooling range (Tom is the equilibrium melting temperature) and f is the corrective factor that takes into account the variation of the equilibrium melting enthalpy (∆Hom) with temperature, defined as 2Tc/(Tc + Tom). For the optimization of the linearization of the data within the temperature range the preferred values of U*, T0, R, kB, Tom, b0, ∆Hom, and σ are 6280 J mol-1,26 328 K (experimental value), 8.32 J mol-1 K-1, 1.38 × 10-16 erg K-1, 593 K (this work), 5.61 Å,25 80 J g-1,8 and 5.6 erg cm-2, respectively.26 Figure 10 shows the LH representation of PPS/IF-WS2 nanocomposites. The growth rate data fit nearly on straight lines, supporting a unique regime behavior of PPS/IF-WS2 nanocomposites. According to the Tc range explored, the crystallization of PPS occurred in crystallization regime III.26 From the slope of LH plots, the values of Kg were calculated and the values of σe were obtained from σσe by substituting Kg. The experimental results indicate that the incorporation of IF-WS2 strongly influence the transport of the PPS chains in the melt region and the formation of the critical nuclei during crystallization. The addition of 0.1 wt % of IF-WS2 increases the σe value of PPS



Figure 10. Lauritzen-Hoffman plots of PPS/IF-WS2 nanocomposites.

Figure 11. POM micrographs of PPS/IF-WS2 nanocomposites at various crystallization times at 264 °C; inset is the plot of spherulite diameter (d) versus time.

from 81 to 89 erg cm-2, which is what supports the slower crystallization kinetics. However, with the increase of the concentration of IF-WS2, the σe value decreases for the nanocomposites (σe ) 73 erg cm-2 for 1 wt % of IF-WS2 and σe ) 41 erg cm-2 for 2 wt %). From these results, we can conclude that lower energy is required to create a new PPS crystal surface at these higher IF concentrations. This observation can also justify the faster crystallization rate of PPS nanocomposites with respect to pure PPS. Polarized Optical Microscopy (POM) Analysis. To support the above conclusion, the crystal growth behavior of PPS/IF-

WS2 nanocomposites has been observed by means of polarized optical microscopy (POM). Figure 11 shows the POM micrographs of nanocomposites taken at 264 °C at different crystallization times. It is clear from the images that the growth rate of the spherulites in the nanocomposite with 0.1 wt % of IFWS2 is similar than that of neat PPS (i.e., same slope of the plot of spherulite diameter (d) versus time for neat PPS and PPS/0.1 wt % IF-WS2). However, the time necessary to reach the same esferulitic size for both samples is much higher in the case of the nanocomposite. This fact suggests that the nucleation process of PPS was retarded, which supports the reduction of

14828 J. Phys. Chem. B, Vol. 112, No. 47, 2008 the global crystallization rate of PPS in the nanocomposite. These results agree with a higher σe. However, when the content of IF-WS2 increased, a larger quantity of crystals was observed with PPS at the same crystallization time. Moreover, no difference could be found from POM micrographs of PPS/IFWS2 (1 wt %) and PPS/IF-WS2 (2 wt %) due to the saturation of the nucleating effect of IF-WS2. These observations are in good agreement with the faster crystallization rates of PPS nanocomposites at these compositions, observed by DSC. Conclusions In the present work, well-dispersed IF-WS2 nanoparticles were melt-mixed with PPS to produce novel PPS/IF-WS2 nanocomposites, and their crystallization behavior was studied from a thermal and morphological point of view. A drastic change from retardation to promotion of crystallization was observed depending on the nanoparticles content, For a low concentration of 0.1 wt % IF-WS2 nanoparticles, the crystallization rate of PPS was retarded. The lower overall crystallization rate observed by DSC was also supported by the higher induction time of nucleation observed from POM as well as by the higher value of the fold surface free energy (σe) of PPS chains calculated from the LH theory. However, when the content of IF-WS2 increased, the PPS/IF-WS2 nanocomposites exhibited faster crystallization rates compared to pure PPS, due to a nucleating effect of IF-WS2 on the crystallization of PPS. In all cases, the crystallization mechanism of PPS related to the n values of Avrami theory was not influenced by IF-WS2. Both neat PPS and PPS/IF-WS2 nanocomposites exhibited double melting behavior after isothermal crystallization at different crystallization temperatures. The two endothermic peaks (TmI and TmII) were related to the melting of the isothermally crystallized PPS crystals with different sizes and degree of perfection and were influenced by the crystallization temperature as well as the IF-WS2 content. On the other hand, the crystalline structure and the equilibrium melting point (Tom) appeared unchanged with the addition of IF-WS2. Moreover, the analysis of the long period (L) of the PPS crystals reflected the same differences observed in the crystallization kinetic data. The reduction of the crystallization rate of the PPS nanocomposite showed a tendency to increase the perfection of the more imperfect crystals (TmI), which caused an increase in the L value of PPS. However, when the acceleration of the crystallization rate of PPS was observed in the nanocomposite, the reorganization (i.e., perfection and thickening) of the PPS crystals was

Naffakh et al. hindered by the IF-WS2. At these compositions, the lower values of L of the PPS crystals were observed with respect to pure PPS. Acknowledgment. M.N. would like to express his sincere thanks to the Consejo Superior de Investigaciones Cientifıćas (CSIC) for postdoctoral contract (I3PDR-6-02), financed by the European Social Fund. This work was also supported by the European Union sixth Framework Program (FOREMOST project under contract NMP3-CT-2005-515840), the European Commission for the X-ray synchrotron experiments performed at the Soft Condensed Matter A2 beamline at HASYLAB (DESY-Hamburg, I-20060118 EC) and the Spanish CICYT for national project (NAN2004-09183-C10-02). The authors would like to thank Dr. S. Funari for his technical assistance in the synchrotron experiments. References and Notes (1) Tenne, R.; Margulis, L.; Genut, M.; Hodes, G. Nature 1992, 360, 444. (2) Rapoport, L.; Nepomnyashchy, O.; Verdyan, A.; PopovitzBiro, R.; Volovik, Y.; Ittah, B.; Tenne, R. AdV. Eng. Mat. 2004, 6, 44. (3) Naffakh, M.; Martıń, Z.; Fanegas, N.; Marco, C.; Go´mez, M. A.; Jimeńez, I. J. Polym. Sci., Part B: Polym. Phys. 2007, 45, 2309. (4) Hou, X.; Shan, C. X.; Choy, K. L. Surf. Coat. Technol. 2008, 202, 2287. (5) Brady, D. G. J. Appl. Polym. Sci. 1981, 36, 23. (6) Cheng, S. Z. D.; Wunderlich, B. Macromolecules 1987, 20, 2802. (7) Desio, G. P.; Rebenfld, L. J. Appl. Polym. Sci. 1992, 44, 1989. (8) Brady, D. G. J. Appl. Polym. Sci. 1976, 20, 2541. (9) Naffakh, M.; Marco, C.; Go´mez, M. A.; Jimeńez, I. Unpublished work, 2008. (10) Avrami, M. J. Chem. Phys. 1939, 7, 1103. (11) Menczel, J. D.; Collins, G. L. Polym. Eng. Sci. 1992, 32, 1264. (12) Ravindranath, K.; Jog, J. P. J. Appl. Polym. Sci. 1993, 49, 1395. (13) Woo, E. M.; Chen, J. M. J. Polym. Sci., Part B: Polym. Phys. 1995, 33, 1985. (14) Silvestre, C.; Di Pace, E.; Napolitano, R.; Pirozzi, B.; Cesario, G. J. Polym. Sci., Part B: Polym. Phys. 2001, 39, 415. (15) Lopez, L. C.; Wilkes, G. L. Polymer 1988, 29, 106. (16) Lopez, L. C. Polymer 1989, 30, 147. (17) Kim, S. P.; Kim, S. C. Polym. Eng. Sci. 1991, 31, 110. (18) Cebe, P.; Chung, S. Polym. Comp. 1990, 11, 265. (19) Chung, S.; Cebe, P. Polymer 1992, 33, 2312. (20) Chung, S.; Cebe, P. Polymer 1992, 33, 2325. (21) Naffakh, M.; Go´mez, M. A.; Ellis, G.; Marco, C. Polym. Eng. Sci. 2006, 46, 1411. (22) Verma, R. K.; Hsiao, B. S. Trends Polym. Sci. 1996, 4, 312. (23) Tabor, B. J.; Magre, E. P.; Boon, J. Eur. Polym. J. 1971, 7, 1127. (24) Lauritzen, J. L.; Hoffman, J. D. J. Appl. Phys. 1973, 44, 4340. (25) Hoffman, J. D.; Miller, R. L. Polymer 1997, 38, 3151. (26) Lovinger, A. J.; Davis, D. D.; Padden, F. J. Polymer 1985, 26, 1595.

JP8063245

Unique Isothermal Crystallization Behavior of Novel Polyphenylene

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